Vector file rendering default settings are found in Edit menu, Preferences, PDF/PostScript. The features contained in this dialog will be applied to vector files only.
Those that affect rendering speed the most are Antialiasing and Resolution fraction.
It is a filter that smooths picture jagged edges. It is disabled by default because uses extra computer resources while rendering vector files to print if enabled. Do not select it unless you are really facing evident aliasing issues, as it slows down neoStampa's printing performance.
It is a factor that decreases image resolution at rendering and thus speeds file processing up. Lower fractions could affect output image quality, making it worse, but this would depend on what kind of details are contained in the picture to print.
The default and recommended value is 1/2.